In a mobile communication system, it is common that a terminal (to be referred to as user apparatus UE hereinafter) and a base station BS performs communication so that communication is performed between user apparatuses UE. However, in recent years, various techniques are considered for performing direct communication between user apparatuses UE.
When performing communication between user apparatuses UE, it is necessary that a user apparatus UE discovers another neighboring user apparatus UE. The present application is on the discovery of the user apparatus UE in this user apparatus UE to user apparatus UE communication.
As a method for discovering a user apparatus UE, there is a method in which each user apparatus UE transmits (broadcasts) a discovery signal including its own ID (identification information). For example, as shown in FIG. 1, in a case where a user apparatus UE-A transmits a discovery signal including its own identification information and a user apparatus UE-B receives the discovery signal, the user apparatus UE-B discovers the user apparatus UE-A by determining that there is the identification information of the user apparatus UE-A in the discovery signal. By the way, as an example, the user apparatus UE-B that has discovered the user apparatus UE-A, directly or via the base station BS, reports, to the user apparatus UE-A, that the user apparatus UE-B has discovered the user apparatus UE-A, so that the user apparatus UE-B communicates with the user apparatus UE-A. As conventional techniques, there are techniques described in patent documents 1-4.